Patent GB-1030590-A (GB)
Title: Controlled-velocity-clutch drive
IPC: H02P29/00
Filed: 1965-04-21
Abstract: 1,030,590. Automatic speed control. EATON MANUFACTURING CO. April 21, 1965 [June 12, 1964], No. 16856/65. Heading G3R. [Also in Division F2] A transistor speed control system for an electromagnetic clutch comprises an adjustable voltage source 15 for producing a reference voltage proportional to a preselected clutch speed, a low pass filter or damping network 16, differential amplifier 19, pulse firing circuit 21 and a solid state switching or control device 23, with load tachometer generator and current feed back loops 25, 27 connected to a summing junction 17 to provide coarse and fine speed control respectively. Circuit details:- The circuit is shown in block form in Fig. 1, component details being illustrated in Fig. 2 (not shown). The adjustable voltage source 15 is provided by a rheostat R5 connected across a constant voltage source, and is applied through resistor RL1 to the low pass filter formed by variable resistor RL2 and capacitor CX1 giving a damped or time integrated reference signal at junction N. The signal is applied to junction 17 through an emitter follower amplifier 18 employing two transistors TRL1, TRL2 connected in cascade, resistors RL1-RL4, blocking diode FL1 and a diode FL2 in series with load resistor RL5 to prevent thermal drift in speed regulation due to variations in ambient temperature. Differential amplifier 19 comprises transistors TR1, TR2 with a common emitter resistor R17 and matched load resistors R11, R13, the junction on C between the latter and capacitor C5 forming the output terminal. The pulse firing circuit 21 is a modified Schmitt trigger circuit comprising transistors TR3, TR4, a common emitter resistor R16, matched load resistors R18, R20, with a coupling network consisting of resistor R19 and shunt capacitor C6. The output is coupled by an isolating pulse transformer to the gate electrode of a silicon controlled rectifier SCR1 constituting the solid state control 23, connected to the clutch coil CL1 through a fuse FU1, contacts E1, resistor R26 and diode F1 A resistor R26 in series with a variable resistance network comprising rheostat R2 and resistor R24 forms the current feedback loop 27. The tachometer feedback is provided by a generator G on the output shaft and feeding an isolation transformer T4 and full wave bridge rectifier F8, the output from the latter being filtered by capacitors C2, C3 and choke coil LL1, and fed to junction 17 through resistors R21, R22 and rheostat R3. Operation:- With potentiometer R5 adjusted to the desired speed setting closing of switch S1 energizes relay coil E and closes contacts E1, E2, the closing of the former connecting clutch coil CL1 and rectifier SCR1 across lines L1, L2, the polarity of diode F1 and rectifier SCR1 being such that coil CL1 can only be energized during negative half cycles of potential across lines L1, L2. Initially transistor TR4 of the trigger circuit is conducting and transistor TR4 cut off, but as the potential across capacitor C5 builds up transistor TR3 is triggered into conduction and transistor TR4 cut off. Decreasing potential at point C then cuts off transistor TR3 to cause conduction of transistor TR4 so that a positive pulse is applied to the gate of rectifier SCR1. As coil CL1 is energized the potential at junction 17 charges capacitor C5 at a rapid rate to increase the power supply to the coil. As the speed increases tachometer generator G applies an increasing negative signal to junction 17 to reduce the conductive periods of rectifier SCR1 and the energization of coil CL1 until the desired clutch speed is attained. The inner feedback loop 27 operates to reduce the response time of the system, sensing the current in coil CL1 to apply a proportional negative signal to junction 17 through rheostat R2 and resistors R24, R26.